Perhaps responding to backlash about preorder items for Battlefield 3, the Battlefield Blog has a FAQ on the Physical Warfare Pack and Back to Karkand pre-order items. They make a point of explaining that the Physical Warfare Pack shouldn't influence game balance in DICE's upcoming military shooter sequel:

Q: Is the Physical Warfare Pack available in all regions, or just in the UK?
A: It will be available worldwide at select retailers. It was first announced in the UK. Exact details for other countries and retailers will be announced at a later date.

Q: Will Physical Warfare Pack imbalance the game?
A: The three exclusive items in the Physical Warfare Pack were specifically chosen not to be overpowered or imbalance or break the game in any way.

Q: Why do I want the Physical Warfare Pack?
A: Owning these items will give you a more varied arsenal, but it will not give you a significant advantage on the battlefield.